Print head motor control with stop distance compensation

Abstract

A control system for a bidirectional printer having a print head carriage movable at different speeds on different printing lines provides for equal stopping distance in the margin at both high and low speed operation. This is accomplished by delaying the initiation of stopping carriage motion when printing at low speed so that the carriage travels farther into the margin and this distance is controlled so as to be equal to the travel distance at the end of a line printed at high speed.

We claim: 
     
       1. A control system for a printer having a bidirectional carriage carrying a print head, said carriage being controllable to print at different speeds on different lines, said printer printing on a medium having a central print area and margin areas on each side of said print area, said system including:   means for generating a command instructing said carriage to stop as it approaches an edge of said print area,   means for measuring the distance traveled by said carriage after said stop command is issued for each line printed, and   means responsive to said measured distance for compensating for any variation of said measured distance from a desired value by issuing said stop command at a different time on the subsequent line of printing.   
     
     
       2. Apparatus in accordance with claim 1 including: store means for storing a measure of any variation from the desired value for use in said compensating on said subsequent line of printing.   
     
     
       3. Apparatus in accordance with claim 2 in which said distance traveled is measured for each direction of printing, and separate values of said variation are stored in said store means for each direction of printing. 
     
     
       4. Apparatus in accordance with claim 3 including a microcomputer for measuring said distance traveled. 
     
     
       5. Apparatus in accordance with claim 3 in which said distance traveled is measured for each direction and speed of printing, and separate values of said variation are stored in said store means for each direction and speed of printing.